The present invention relates to flash memory devices and, more particularly to a method of manufacturing a flash memory device in which a contact plug used to an upper line and a lower line is formed to have an angular shape (e.g., rectangular-like shape).
As the design rule of devices decreases, the following may occur in the process of forming the drain contact hole.
First, in the process of forming the drain contact hole using a rectangular mask, the drain contact hole becomes circular due to exposure properties, such as a proximity effect and aberration.
Second, the circular drain contact hole formed above can be difficult to control the roughness near the edge portion of the contact hole. Thus, the uniformity among the drain contact holes may be difficult to obtain.
Third, in the drain contact hole having a circular shape, bias control in the long axis and the short axis can be difficult.
Fourth, an etch process may not be properly performed when the drain contact hole is formed in a circular shape in sub-100 nm design due to the limit of the resolution of exposure equipment employing a source such as ArF or KrF.